About two weeks ago I put 6 eggs in my homemade incubator for a science fair experiment. I found it was very hard to regulate the temp. The humidity was very low them first few weeks. I've done some research and found some things to help the regulate things.
Humidity- boil water and poor into a wide dish to raise. To lower humidity put normal water in and a small dish in.
Temp- Do not let the temp raise over 104. My incubator has been at 104F 4 times. I have also read about a woman who had a temp spike at 134 and she still got one chick! Before you leave the house make sure that the incubator is at 97-99 (depending on the weather outside and the heat in the house. My incubator has been down to 91-104.
Do not expose incubator to drafts and sunlight. Turn eggs 3 times a day but only turn a quarter. Some hatches have been better not turning the eggs at all! Some have had a better hatch if they only turn 1/2 once a day. I was scared to do that because i read that the cord from the membrane can wrap around the chicks head and make it very hard to hatch!
Update: the eggs hatched on the 23 day so do not throw out. I made a mistake. When the last egg was hatching I opened the cover and dried it out! That day we lost 3 eggs out of 6. The best way was when we turned the eggs 1/2 a turn instead then 1/4 turn. I have 3 happy chicks out of my incubator. I still can't believe that it was going to work out! I if i could, i would do it again. it was really fun!